Petroleum based lubricating oils are mixtures of liquid hydrocarbons having a requisite viscosity for proposed end use lubrication applications. As terminology has been developed in the art, lubricating oils frequently are classified as either naphthenic lubricating oils or paraffinic lubricating oils.
By a generally accepted consensus, paraffinic lubricating oils have a hydrocarbon content containing at least about 50 volume % paraffinic hydrocarbons and less than about 25 volume % naphthenic hydrocarbons. Such lubricating oils also may contain small to modest concentrations of aromatic hydrocarbons, and heterocyclic compounds. The oil also will contain lubricating oil additives. By a similar consensus, naphthenic lubricating oils have a hydrocarbon content made up of at least about 30 volume % naphthenic hydrocarbons, with the balance of the hydrocarbons being predominantly aromatic hydrocarbons, but which also may contain small to moderate quantities of paraffinic hydrocarbons and heterocyclic compounds. The oil also will contain lubricating oil additives.
Historically, naphthenic lubricating oils have been the lubricating oils of choice on a cost/performance basis. This has been particularly the case in formulating highly viscous oils used in heavy duty applications such as railroad and marine diesel engines. It has been the experience in the art that the naphthenic lubricating oils have the capability of dissolving and/or softening significant quantities of the semi-solid carbonacous decomposition products which form in crank cases under severe operating conditions. The semi-solid carbonacous components formed on the cylinder walls and suspended in naphthenic lubricating oil in the crank cases of diesel engines tend to be softer than the corresponding carbonacous products formed in paraffinic lubrication oils under identical operating conditions. By reason of their softer nature, the deposites formed from naphthenic lubricating oils cause less wear on moving engine parts. It is the belief in the art that diesel engines have a longer operating life when lubricated with naphthenic lubricants than is the case with paraffinic lubricants. Specifically, it is believed that the incidence of piston ring breakage is lower when naphthenic lubricating oils are employed.
By a quirk of nature, naturally occurring crude oil containing significant fractions of naphthenic hydrocarbons in the lubricating oil range are found largely within the continental United States and Venezuela. Crude oils produced in other oil producing areas of the world have relatively lower concentrations of such naphthenic hydrocarbons. Accordingly, as the worldwide demand for naphthenic lubricating oils is increasing, the available supply of crude oils containing significant concentrations of the desired naphthenic hydrocarbons is decreasing. It is thus seen that a shortage of naphthenic lubricating oils is developing.
For the above reasons, there is a need in the art for developing processes to enhance the volume of naphthenic lubricating oils that can be produced from existing crude oil supplies.